1. Technical Field
The present invention relates to a MEMS structure and a manufacturing method thereof, more particularly, to an optical modulator and a manufacturing method thereof.
2. Description of the Related Art
MEMS refers to a microelectromechanical system or element, which is a technology that uses semiconductor manufacturing technology to form three-dimensional structures on silicon substrates. There are a variety of applications in which MEMS is used, an example of which is the field of optics. Using MEMS technology allows the manufacture of optical components smaller than 1 mm, by which micro-optical systems can be implemented. Micro-optical components such as optical modulators and micro-lenses, etc., corresponding to micro-optical a system, is selected for application in telecommunication devices, displays, and recording devices, due to such advantages as quick response time, low level of loss, and convenience in layering and digitalizing.
The optical modulator is a circuit or device which loads signals on a beam of light (optical modulation) when the transmission medium is optical fiber or free space in the optical frequency range. The optical modulator can be divided mainly into a direct type, which directly controls the on/off state of light, and an indirect type, which uses reflection and diffraction, where the indirect type may further be divided into an electrostatic type and a piezoelectric type according to how it is operated.
Regardless of its operation type, the indirect type optical modulator performs optical modulation by means of interference occurring due to the differences in paths between lights reflected or diffracted on different surfaces. Thus, the optical modulator necessarily requires a reflective layer for reflecting or diffracting light, and in order to improve the light diffraction efficiency of the optical modulator, the surface properties of the reflective layer must be maximized.
However, surface deterioration of the reflective layer is increased by heat generated during the process of forming the reflective layer or during subsequent manufacture processes, and stress changes in the reflective layer dependent on changes in temperature are also greatly increased.
Further, the ambient humidity generated during the process of forming the reflective layer or during subsequent manufacture processes causes the surface of the reflective layer to be oxidized.
Such deterioration in surface properties of the reflective layer has adverse effects on the light diffraction properties of the overall optical modulator, and lowers its reliability.